Oscillation generator



Jan. 19, 1932. w. A. MARRisoN 1,841,489

OSCILLATION GENERATOR Filed March 24, 1928 A TTDR/VEY i UNITED-STATESfPArENr fate `Patented Jan. 19, 1932 te@ f WARREN A. .MARRISON orORANGE, NEW JERSEY, AssIGNoR To vBELL TELEPHONE? LABORATORIES,INCORPORATED,- oE NEW YORK, N. Y., A CORPORATION OE NEW OSOILLATIONGENERATOR y Applicatin' iearmamn 24, 192s. serial No. 264,432. y

VThis invention relates to oscillation generators and particularly-tosystems for generatingoscillations of constant frequencywhich areindependent of temperature variations.

For some purposes itis desirable' to generi a wave whose frequency isconstant within very narrow limits. One of the difliculties to beovercome in the .production ofv oscillations of constant frequencyis thevariations in frequency which occurl with changes In temperature withany system where no means ior compensating for temperature variations isprovided. In the absence of such compenf order to sating means it isnecessary to take elaborate precautionsl to maintain the frequencycontrolling means'at a constant temperature in o f A feature of thisinvention is the provision ciprocal of the ratio of of two temperaturecompensatingmechanical 4vibrating elements, the frequency of vibrationyof each of whichV controls the'generation of oscillations. Theseoscillations arecombined to produce lfurther oscillations, thefrequencyof which isequal to the sum .ordiffeb ence of those firstgenerated, andfis constant. Another feature of the invention is theprovision of two mechanical vibrating elements having temperaturecoeiiicients of frequency the ratio of which is equal to the rethefrequencies at which they are vibrating.

According to thepresent invention a constant frequency. is obtained,irrespective of temperature variation, by theuse of :two vibratingsystems having Ytwo control members with different temperaturecoefficients of frequency. Any desired frequency may be obl tained, as aysum or differencefrequency between the two systems, by choosing valuesof frequency for the control members such that the ratio of thefrequency of their vibrations is equal to the reciprocal of the ratio oftheir temperature coeiiicientspof frequency.

- The drawing illustrates two spaceV discharge tubes 1 and 2 each havingan input circuit and. an output circuit. The input and `tionsof adiiferent prevent variations in frequency of YThat is, the oscillatorcontrolled by the vibrating element 3 will produce oscillations of onefrequency and the oscillator controlled by the vibrating element 4 .willproduceoscillafrequency. ThQOutput circuits of the respective spacedischarge tubes include electroma netic devices 5 and 6 and coils fand8; pace current issupplied to the tubes l and 2 from a common source 9.l l The respective input circuits include, electromagnetic devices and11, and acommon sourcer12 forsupplying biasing potential to theirgrids.. v f i The filaments of the tubes are supplied with heatingcurrent by a common battery 13. As so far described the operation of thei system is as follows r`Assuming that the mechanical elements arevibrating, current in the output of the'spacedischarge tubes l and 2will 5 and 6 and maintain the mechanical elements 3 and 4 vibrating'attheir natural frequencies. Potentials of these frequencies, picked vupby the eleotromagnets y10 and 11 included in the respective inputcircuits of the space discharge tubes, will be impressed on therespective grids. f f

Coils 7 and 8 are inductivelyA coupledto a secondary winding ycircuit ofa third space discharge device which servesto combine the waves of thetwo frequencies impressed upon its grid to produce oscillations havingfrequencies equal to pass through the electromagnets 14, included in theinputY the sum and difference of the frequencies of f and a battery 20for supplyino space current to the device.

The circuit 18, 19 is tuned to the sum or difference frequency of thetwo impressed waves. Energy of the wave selected is inductively suppliedthrough the coupling 19--21 to a load circuit.

For the purpose of illustrating the operation of this invention let itbe assumed that mechanical vibrating element 3 has a natural frequencyof 300 cycles per second and that mechanical vibrating element 4L hasanatural frequency of 200 cycles per second at a given temperature. Alsolet it be assumed that the temperature coefficients of frequency ofthose elements are, respectively, A and 3/2 A. Then at any temperaturethe frequency of element 3 will be equal to 300 (1-*At) and thefrequency of element a will be equal to 20o (i-s/e ai),

where t is equal to the diHerence between the temperature at which theelements 3 and 4 have a natural frequency of 800 and .200 cycles persecond, respectively, and a common operating temperature at any instant.The difference of these frequencies is 100 cycles per second and doesnot vary with temperature. The 100 cycle componentwill be selected bythe tuned circuit 18, 19 in the output circuit of the modulator.

In the operation of the system described above, if one oscillator iscontrolled by a mechanical element of frequency f1 having a coefficientof a, and a second oscillator is controlled by a second mechanicalelement of frequency f2 having a coefficient Vthen f1(1 1t)f2(1t)= I ifffr1 2lf:f

That is, the condition for f to be independent of temperature is thatf1af2=0, that The condition identified by the above formula holds forall cases.. whether the temperature coefficients of the controllingelements are of the same or of opposite sign.

In the case where the temperature coefficients of the control elementsare of opposite signs it is necessary to select the sum of thefrequencies produced by intermodulation of the controlled wave. 1n thatcase it now be assumed that being used to control and For example, letquartz resonators are the frequencies of the two sets of oscillationsand that one control element, having a positive coefficient of 9 10r isvibrating at a frequency of 1,000,000 cycles per second and the othercontrol element having a negative coefficient of 3X10'5, is vibrating ata frequency of 3,000,000 cycles per second. For each degree rise intemperature the first control element will increase its rate ofvibration 90 cycles per second, while the second element will decreaseits rate of vibration 90 cycles per second. Therefore, a wave obtainedas a product of intermodulation of these two waves will remain constantat 4,000,000 cycles per second regardless of temperature variations.

In order that the system described above may operate to produceoscillations of constant frequency, it is only necessary that the ratioof the temperature coefficients of frequency of the two mechanicalelements equal the reciprocal of the ratio of the two frequencies.However, this does not make it necessary to use a material having aselected temperature coefficient of frequency in order to produceoscillations of a desired frequency. For any two different temperaturecoefficients, it is always possible to choose two frequencies such thattheir sum or difference is `any desired pendent of the temperature ofthe two elements. For example, if the temperature coefficients offrequency of the elements were as in the first example given, A and 3/2A, and it was desired to produce a constant frequency of 1,000 cyclesper second, it would only be necessary to adjust the vibrating elementsto have natural frequencies of 3,000 and 2,000 cycles per second,respectively. 1f a frequency of 1,100 cycles were desired, the elementswould be adjusted to 3,300 and 2,200 cycles respectively.

When it is desired to produce a relatively high constant fre uency withelements having temperature coe cients of like sign, it is desirablethat the coefficient-s differ by a considerable amount, say in order tokeep the control frequencies from being too high.

However, the operation of this invention with elements of like sign isnot limited to low frequenciesas the temperature coefficients offrequency of different quartz crystal resonators may vary in the ratioof 3 to 1 or more. Thus, it will be seen that the upper limits offrequency which this device is capable of producing with elements oflike sign is very high, and with elements of opposite sign is muchhigher.

Of course, in a system embodying the invention, it is necessary tomaintain the control elements at the same temperature, so that oneelement does not vary more than the other. This presents no difficulty,since it can be taken care of by mounting both elements on the same baseand enclosing them to prevent uneven circulation of the air around them.

frequency and is indc- W'ith the devices. of the present invention,power Huctuations will notaifect the sum or difference frequencies toany great extent. If the two elements were driven by separate powersources, it would be expected that variations in frequency inthis systemdue to `fluctuations in power would be considerably greater than thevariations in a directly driven system, because variations due to the fpower supplied by the separate sources would at times add. If bothelements are operated from the same power source,however, variations infrequency will, tendV in the same direction in both elements and thefrequency variations ywill be approximately the same as in a systemdriven directly.

kW'haty is claimed is: Y y n l. An oscillation source comprising anoscillator controlled bya mechanical vibrate ing element, and a secondoscillator controlled by a second mechanical vibrating element,

the ratio of the frequencies of vibration of the mechanical elementsbeing equal to the reciprocal of the ratio of their temperaturecoeilicients of frequency. y

2. Asystem for producing oscillations of a desired constant frequencycomprising wave producing means, including mechanical vibrating'elements the ratio of whose frequencies of vibration is equal to thereciprocal of the ratio of their temperature coefficients lof frequency,for determining the frequencies of two Waves whose frequencies differ bythe desired frequency, and means for combining said waves.

3. In combination an oscillating systeml comprising an oscillatorcontrolled by a me-V chanical vibrating element at a frequency whosetemperature"coefcientis Am, and a second oscillator controlled by amechanical vibrating element at a frequency y and whose temperaturecoefficient of frequency is n, where p Y el.

'y m 4. Any oscillating Asystem comprising an oscillator the frequencyof whose oscillations is controlled by a mechanical vibrating element, aysecond oscillator the-frequency of Whose oscillations is controlled bya second mechanical vibrating element, the frequency of the vibration ofthe second element with respect to the first being'equal to the recip-:1 rocal of the ratio of its temperature coefiicient of frequency withrespect to the first, and armodulat'or for combining Waves of thefrequencies of the two mechanical vibrating elements to produce aconstant frequency.

In witness whereof, I hereunto subscribe my name this 22 dayy of March,y1928.

WARREN A. MARRISON.

